Tractor hydraulic system



Oct. 29, 1957 E, c. MCRAE 2,811,016

TRACTOR HYDRAULIC SYSTEM Filed Jan. 3, 1955 2 Sheets-Sheet 1 IMP/4C T E C MCRA E INVENTOR.

F/GIZ ATTORNEYS Oct. 29, 1957 E. c. MCRAE 2,811,016

- TRACTOR HYDRAULIC SYSTEM Filed Jan. 3, 1955 2 Sheets-Sheet 2 E. CMcRAE INVENTOR.

'ATTORNEKS United States Pa fi ,0 p

TRACTOR HYDRAULIC SYSTEM Edwin C. McRae, Dearborn, Mich., assignor to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Application January 3, 1955, Serial No. 479,492

3 Claims. (Cl. 60-52) This invention relates generally to tractor hydraulic systems, and more particularly to systems of the type wherein the fluid output of a constantly operating pump is either bypassed to a sump or is directed to a lift cylinder connected to an implement to lift the latter.

An object of the present invention is to provide a tractor hydraulic system in which protection is afforded to the hydraulic system and to the tractor components against damage resulting from impact loads imposed upon the lift or ram cylinder by the implement. Conventional hydraulic systems for tractors employ a pressure relief valve in conjunction with the lift cylinder to protect the system. Such a relief valve, however, is subject to the pump pressure, and must therefore be set high enough to open only above the maximum pump pressure. The maximum pump pressure during the initial portion of ,the lift cycle is always considerably higher than the ram static pressure because the inertia of the implement'must' be overcome and because additional pressure is required to break the implement loose from the soil. Conse-' quently, when the bypass connection to the sump is closed the initial build-up of pressure must be considerably higher than the static pressure in the ram cylinder. Accordingly any relief valve in the ram cylinder must be set high,

enough to prevent operation of the valve during the lifting cycle. If not, damage to the valve will result and cause its premature failure. With the conventional relief valve set to open only at a pressure higher than maximum pump pressure, it is ineffective to discharge fluid from the ram cylinder when impact loads are imposed upon the ram cylinder during transport of heavy implements.

In the construction of the present invention a static. pressurerelief valve is provided which is substantially balanced insofar as pump pressure is concerned and con- Since the sequently is inoperative during the lift stroke. valve is unaifected by pump pressure it may be set to open at a pressure only slightly above the maximum static load to be lifted and consequently is responsive to impact loads placed upon the ram. cylinder by the implement even though such loads are only slightly greater than the nor-' mal static load. Maximum protection is thus afforded to the tractor and implement.

A further object of the invention is to provide, in a to, the sump to thusgprotectthe system againstdamage due to excessive pressures. The static pressure relief valve also incorporates a check valvepermitting the discharge of fluid from the pump to the ram cylinder during the lift stroke, providing a compact and inexpensively manufactured unit.

Other objects and advantages of this invention will 'be" mademoreapparentas this description proceeds, particularly when considered in connection with the accompanying drawings, whereint r 2,8 l l ,015 Patented Oct. 29, 1957 Figure 1 is a semi-diagrammatic cross sectional .view

' of the construction of the present invention, with the Figure 3 is a semi-diagrammatic cross sectional view,

similar to Figures 1 and 2 but showing the valves in lowering position.

Referring now to the drawings, the reference character ll-indicates a lift or ram cylinder having a piston 12 and a control valve 19, respectively.

slidable therein and acting upon a piston rod 13 adapted to be connected in a conventional manner to an implement to lift the latter when fluid under pressure is supplied to the cylinder 11.

A valve housing 14 is carried by the tractor and is positioned in overlying relationship to a sump so that fluid discharged from the housing is returned to the sump. The housing 14 is formed with a pair of valve bores 16 and 17 arranged to receive a static pressure relief valve 18 The bore 16 in the valve housing is formed with'a reduced end extension 21, and the shoulder between the two portions of the bore is tapered to form a conical valve tion 24 extending integrally therefrom and formed at its end with a conical nose portion 26 adapted to engage the valve seat 22. A heavy coil spring 27 biases the relief. valve. to the left as shown in Figure 1 and is seated against a plug 28 in the end of the bore. A backing plate' 29 is provided for the valve housing.

The relief valve 18 is formed with'a cross port the body 24 of the valve intersecting an axial passageway 32 extending completely through the valve and terminating atits left end in a conical valve seat 33. A ball check pair of axially spaced enlarged integral lands 43 and 44' arranged to control respectively a discharge passageway valve 34 is positioned in the reduced end extension 21 of thebore 16 and is arrranged to be biased toward the valve seat 33 in the relief valve 18 by means of a coil spring 36.

The valve housing 14 is formed with a pump output conduit 37 providing communication between a conven-L tional pump (not shown) carried and driven by the tractor, and the relief valve bore 16. The valve housing is also'formed with a ram supply conduit 38 leading from the reduced end portion 21 of the valve bore to the ram the valve bore 17 in the valve housing and is provided with an end portion 42 extending exteriorly of th valve housing for connection to suitable control linkage tor actuation thereby. The control valve 19 is formed with a 46 and the bypass conduit 39.

Figure 1 illustrates the position of the valves during a lift stroke. It will be seen that the control valve 19 has been moved to a position wherein the end land 44 closes the bypass conduit 39 thus preventing the discharge of fluid from the pump output conduit 37 to the sump. Pump pressure is immediately built up and fluid from the pumpoutput conduit 37 is directed through the ports 31 and the K axial passageway 32' in the relief valve 18 to unseat the check valve ball 34 from its seat 33 against the action of spring 36. Fluid from the pump is thus directed to the mini-cylinder 11 to lift theirnplementl It will benoted that at this time the land'43 on the control valve 19 During the lift operation fluid from the pump output conduit 37 communicates through the ports 3t and axial passageway 32 formed in the relief valve 18 to the chamber between the head 23 of the relief valve and the plug 28. Pump pressure is thus impressed upon the entire right hand face of the head 23 of the relief valve. It will be noted, however, that pump pressure is exerted; against the exposed annular portion at the left, handlface of the head 23 of the relief valve, and also is exerted against the left hand end of the reduced body portion, 23 of the valve, communication to this portion of the valve being through the ports 31 and passageway 32 past the open, check valve 34. As a result of this arrangement the relief valve 18. is substantiallybalanced insofar as pump Pressure is concerned; During lifting, therefore, the, relief valve 18 is.held against the valve seat 22' by the coillspring 27 regardless of'the magnitude ofthe. pump pressure...

When the tractor is being used to transp'orhheayy implements over rough roads orroughterrain, severe impact loads are impressed upon the tractor linkage and, -ifhigh enough, the links may be bent or the ram cylinders damaged. In addition, the high pressures created in the, ram cylinder by the impact loads may be detrimentaltoother components of the hydraulic system. The present construction absorbs these impact, loads and thus protects the tractor and implement. When the pressure in the. ram cylinder increases above the normal static pressure the entire relief valve 18' is moved to the right against the actionof coilspring 27 to open the. valve seat 22. and permit fluid to be quickly discharged from the, rarnlsupply conduit 38. past the relief valve 18 to the bypass conduit 39 leading to the sump. The ram pressure is, exerted against the exposed end of the body portion. 24 of, the relief'valve, and the spring. 27 is of predetermined size such that a pressure only slightly above the maximum static load to be carried will be sutficientto openthe relief valve. Inasmuch asthe-cross. sectional area of a portion 2 1 of thevalve bore is adequate to permit. the quick. discharge of a substantial quantity of fluid from the ram cylinder, sufiicient fluid may bev discharged past the relief valve 18 to properly absorb all impact, loads. chattering of the relief valve against its seat is minimized with the present construction by the provision of a conicaliengagement between the valve and. its seat, since the ram pressure is, exerted upon a larger valve area as soon as the valve, is moved slightly from its seat, enabling thevalve to remain open. until the: impact load. has been absorbed and the pressure-in the ramcylinder sufficiently reduced.

Figure 2,illustrates the; position of the relief valve 18 after it has been moved from its seat 22 by an impact load resulting in an increased pressure in theram cylinden At this time, of course, the check valve 34 is inengagement with its seat 33, and the control valve 19 is positionedto permit discharge of fluid through the bypass conduit; 39 to the sump.

Figure 3 illustrates the positions ofthevalves during lowering of the implement. The control valve is moved to a position uncovering the discharge passagewayv 46 tov permit passage of fluidfrom theram cylinder 11 to the. sump to lower the implement. The. check valve 34 and. the relief valve 18 remain seated, and pump output fluid is discharged tothe sump through conduit 39.. i

It will be understood that the invention is not to; be limited to the exact construction shown and described, but that various changes andmc-difications may be-rnade; without departingfrom the spirit and scope of; the invert: tion, as. defined in: the appended-claims.

Whaeis claimedis:

1'. In, a. tractor hydraulicsystem for raising; anddowering an implement carried-by the tractor, apumpgasump, a lift cylinder operativelyconnected to. said? implement, a valve. housing having an. inlet port. connected: to said, pump, return means connectedto saidf sump aridQanaoute let port connected to. said" lift cylinder, a first valvetres ciprocably mounted in said housing and: movable: to. a;

. in said first position, spring means biasing said second valve toward a closed position preventing fluid from being freely discharged from saidoutlet port to said return means, said. second valve having a part thereof exposed to the fluid pressure in said inlet port to maintain said second valve closed, whensaid first valve is insaid second position during the lift stroke of the system regardless of pump pressure, said second valve having another part thereof exposed to the fluid pressure in said outlet port to open said second valve and permit the discharge of fluid from said. outlet portto said return means when said first valve is in said first position upon a predetermined increase in the fluid pressure in said lift cylinder resulting from an impact load, said second valve being formed with an axially extendingpassageway therein communicating with said inlet. port and said. outlet port, and a spring biased check valve normally held in engagement with a valve seat on said second valve to close said passageway in said second valve but adapted to be unseated against, said springupon a pressure build-up insaid inlet port to permit the passage of fluid from said inlet port to said outlet port when said first valve is closed.

2". In a tractor hydraulic system for raising and lowering an implement carried by the tractor, a pump, a sump, a lift cylinder operatively connectedto said implement, a valve housing having avalve bore therein, said valve borehaving a large diameter portion and a small diameter portionwith a valve seat formed at the juncture between said portions, said valve housing having a passageway therein. leading from, the. small portion of said" valve bore and connected to said' lift cylinder, a second passageway leading from the large portion of said valve bore and connected to said pump and a. third passageway leading from the large portion of said valve bore and] connected to said sump, a.relieffvalve,reciprocable Within the large portion oflsaid valve bore, andhavi'ng a body portion of smaller diameter than the large diameter portion of said valve bore, to. form an, annular chamber communicating with said second; and: third passageways, the end portion of the. smaller diameter, body portion of, said relief valve being engageablewith,saidvalve seat, a, coil spring biasing said. relief, valve toward said, valve seat, said relief valve having anenlarged head, at the end of, the body portion remote frornsaid'. valve seat of; a. diameter correspon ing to'the diameter of the largeportion of said: valve bore. said. relief, valve having. apassageway through the head thereoflestahlishing communication, between said second passageway and the. end of said, valve bore beyond said relief valve, and to maintain said, relief valve in engagement with. said. valve, seat, during the lifting of. said implement but to enable, said relief valve to be moved away from said seat by an increasedi'mpact pressure in the smallportion of, said, valve bore to establish, communication between, said firstand third passageways to discharge. fluid from said liftcylinder, during impact loads.

3. In a tractor hydraulicsystem for raisingand lowering-an implement carriedlby. the tractor, a pump, a sump, a, lift cylinder operatively connected. to. said. implement,

ageway therein leading front-thesmall; portion; ofv said valve bore and connected to said lift cylinder, a second passageway leadingifrom the. large. portion; of said. valve bore; and;connected; to saidz-pumpand; a third passageway leading from the large portion ofixsaid; valve bore; and

connected to said sump, a relief. valveireciprocable within 5 the large portion of said valve bore and having a portion at one end thereof engageable with said valve seat, a coil spring biasing said relief valve toward said valve seat, and said relief valve having passageways therein establishing communication between the end of said relief valve remote from said valve seat and said second passageway in said valve housing to maintain said relief valve in engagement with said valve seat during the lifting of said implement but to enable said relief valve to be moved away fromsaid seat by an increased impact pressure in the small portion of said valve bore to establish communication between said first and third passageways to discharge fluid from said lift cylinder during impact loads,

said relief valve having an axial passageway extending completely therethrough and a radial port communicating with said axial passageway and with said second passageway, a check valve ball in the small portion of said valve bore engageable with the end of said relief valve to close said axial passageway, and a spring in the small portion of said valve bore biasing said check valve ball toward said relief valve.

References Cited in the file of this patent UNITED STATES PATENTS 2,506,008 Arps May 2, 1950 

